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How Large Should My Furnace Be?
Posted On: November 13, 2024
The size of a furnace is typically measured in BTUs (British Thermal Units), and the right size depends on various factors such as the size of your home, your climate zone, insulation quality, and the number of windows and doors. Here's a breakdown of what to consider when determining the appropriate furnace size:
1. Square Footage of Your Home
- Generally, you can calculate the BTUs needed based on your home’s square footage. As a rule of thumb, most homes need between 30 to 60 BTUs per square foot.
- For example, if your home is 2,000 square feet, a rough estimate for furnace size would be
- 2,000 sq ft×40 BTUs per sq ft=80,000 BTUs2,000sq ft×40BTUs per sq ft=80,000BTUs
2. Climate Zone
- Warmer climates require fewer BTUs per square foot, while colder climates need more.
- Here’s a rough guide by climate:
- Warm climates (like Florida): 30–35 BTUs per square foot.
- Moderate climates (like the Midwest): 40–45 BTUs per square foot.
- Cold climates (like New England): 50–60 BTUs per square foot.
3. Insulation and Windows
- If your home has good insulation, you might need fewer BTUs. Poor insulation or old, drafty windows can increase the BTU requirements.
- High-quality windows, doors, and insulation can reduce the furnace size by 10–20%.
4. Ceiling Height
- Most BTU estimates assume an 8-foot ceiling. If your ceilings are higher, you may need a larger furnace to heat the increased volume of air.
5. Furnace Efficiency
- High-efficiency furnaces produce more heat per BTU, so you can often go with a smaller size if you’re choosing a furnace with an efficiency rating of 90% or higher.
Example Calculation:
Let’s say you have a 2,000-square-foot home in a moderate climate with good insulation and standard 8-foot ceilings. You might aim for around:
2,000 sq ft×40 BTUs per sq ft=80,000 BTUs2,000sq ft×40BTUs per sq ft=80,000BTUs
If you choose a high-efficiency furnace (like 90% AFUE), you could reduce the size to around 72,000 BTUs.
When in Doubt, Consult a Professional
A qualified HVAC contractor can do a more precise calculation called a Manual J load calculation, taking into account all relevant factors, and recommend the right furnace size. This prevents you from oversizing or undersizing, which can lead to inefficiencies and comfort issues.
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See What Our Customers Are Saying:
Aug 8, 2025
We are very happy to recommend this company to everyone. Our furnace broke down on Sunday morning. We phoned them and before noon Grant the owner showed up. He worked on the furnace for about a hour not wanting to give up to fix the problem. The furnace was 17 years old. I was the one talking about replacing it. End result was the next day it was all done. On the Sunday Bob came over with heaters to warm up the house. We decided to replace the water heater at the same time. Thanks Grant for the excellent work. Thumbs up.
Aug 8, 2025
Right on time. Explained how to work the HRV in a different way so the house would not be so dry. Changed my whole house water filter for me as well. Friendly, helpful, caring service!
Feb 18, 2025
Very pleased with the professional service that TwinTech Heating and Cooling provided in replacing my furnace. I got several quotes from different service providers. Their price was excellent and they explained the features very well. We are very glad we went with TwinTech and highly recommend their services.
Feb 18, 2025
We were new homeowners in need of a second opinion. TwinTech Heating & Cooling were Amazing and professional. Very knowledgeable and great service all around. Recommend to anyone looking for honest and reliable services. Treated with respect and care. Thank you Greg, Mitch and Bob!
Feb 18, 2025
TwinTech is an excellent and honest company! I called them for a second opinion after being told by another company that I needed to replace my furnace. Turns out this was not the case at all! I did not need a new furnace. TwinTech did not push to make an unnecessary sale and saved me from a huge expense. Bob and Mitch were extremely professional and above all honest! I definitely recommend TwinTech!
Feb 18, 2025
Amazing experience with TwinTech Heating & Cooling! Their team was professional, knowledgeable, and efficient from start to finish. They installed my new furnace quickly and left everything spotless. The technicians took the time to explain everything and made sure I was comfortable with the system before they left. Great customer service and fair pricing. I highly recommend them for anyone needing HVAC services!
Feb 18, 2025
Great experience all around. Bob was sharp and easy to talk to, and Greg handled the installation perfectly. Would hire them again in a heartbeat.
Aug 17, 2024
I returned from vacation to find my AC unit on the Fritz. After calling way too many places I connected with TwinTech. Ive used the company in the past for my furnace so I was happy when I recognized Greg at my front door. Hes great and the service is always top notch. Id highly recommend using twintech for honest, superior service in the Durham region. Thanks!
Aug 13, 2024
I called Twin Tech when my air conditioning stopped working. Greg came over to diagnose the issue - the same day. He was able to diagnose the issue and resolve it quite quickly. Although it was a quick fix, Greg was very thorough in explaining the issue and provided great advice. Not to mention, I felt very comfortable having Greg in my home - which I consider very important when hiring a service provider. Twin Tech will be my go-to from now on. Thank you!!
Aug 12, 2024
Just hired TwinTech Heating & Cooling to do an A/C Unit removal & reinstall to allow for landscaping access on the side of my house, and they were wonderful!
Bob, Greg & Mitch make a great team! Quick appointment times, super knowledgeable, expert troubleshooting capabilities & very customer service oriented.
I would highly recommend them for all of your HVAC needs! Great job guys!!
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